The present invention relates to a cathode assembly of an electron gun for a color cathode ray tube having an improved heater support structure, and more particularly to a cathode assembly of an electron gun for a color cathode ray tube, in which assembling of the heater is facilitated and stability in view of the structure is improved.
The electron gun for a color cathode ray tube (CRT) has three cathodes for generating three electron beams, and a plurality of grids and electrodes for controlling the electron beams. The cathode emits thermal electrons for producing the electron beams, having a thermal electron emitting material layer which is a thermal electron emitting source and a heater which is an energy source for heating the thermal electron emitting material layer.
The electron gun is provided at the rear end of a funnel which constitutes a vacuum vessel in cooperation with a panel, and shoots the electron beams on a screen provided in the funnel. Generally, at the rear side of the funnel is provided a cylindrical neck which houses the electron gun.
Referring to FIG. 1 which shows a part of an electron gun for a general CRT, the electron gun for the CRT includes cathode 8 which is a thermal electron emitting source, two grids G1 and G2 which produce the thermal electrons as electron beams, and a plurality of focus electrodes G3 and G4 for accelerating and collecting the electron beams. As shown in FIG.2, cathode 8 has a cylindrical sleeve 8a in which a heater 9 is internally installed, and a cap type base metal 8b of which the surfaces are coated with thermal electron emitting material 8c. A heater supporter 10 for supporting heater 9 in cathode 8 is located near the upper portion of a stem 7 having a plurality of lead pins 7a for electrical connections.
The above elements are located in a predetermined distance between two parallel bead glasses 6, and are fixed to bead glasses 6, to thereby form a complete electron gun.
In the electron gun having the above-mentioned structure, the fixed position of heater 9 which supplies the thermal energy to the cathode has a large influence on various properties of the entire electron gun. Accordingly, when heater 9 is welded in supporter 10, a high degree of precision is required.
However, since the conventional electron gun has a heat support structure of an inferior structural stability and degree of precision, the heater cannot be supported precisely and stably. Accordingly, the properties of the entire electron gun are adversely affected.
Referring to FIG. 3, the conventional heater supporter 10 has four Z-shaped fixed pieces 11 and 11' which are symmetrically installed between two pieces of bead glass 6 which are located in a predetermined distance from either side of heater supporter 10, two substantial V-shaped first connection pieces 12 which are welded in the free ends of first two fixed pieces 11, and two second connection pieces 13 which are welded in the free ends of second two fixed pieces 11'. The outer ends of first connection pieces 12 and the free ends of second connection pieces 13 are arranged such that there is sufficient space between them, so that both end terminals Ha of heater 9 can be welded and supported to the outer end of first connection pieces 12 and the free ends of second connection pieces 13. The inner ends of first connection pieces 12 are spaced similar to the spacing between the outer ends of first connection pieces 12 and the free ends of second connection pieces 13.
Such a heater supporter of a conventional electron gun for a CRT is composed of a number of components such as two pairs of fixed pieces, one pair of first connection pieces, one pair of second connection pieces, etc. Accordingly, the structure is complicated, the assembly work is difficult and the consumed manpower cost is high.
Also, since the fixed pieces and the first and second connection pieces have a number of bent portions, it is not only difficult to fix the heater at a predetermined position, but also it is difficult to fix the heater at the center of the sleeve of the cathode. Accordingly, the CRT is slow to provide an initial picture image, and the white balance is lowered.